1. Field
Embodiments of the invention relate to a multilayer optical sheet module, more particularly, to a multilayer optical sheet module that improves durability by increasing an adhesive area and improves brightness simultaneously.
2. Background
A liquid crystal display device is a display device used in a notebook, a personal computer, a smart phone or a TV. With expanding demands for liquid crystal display devices, characteristics of liquid crystal display devices have been improved.
A liquid crystal panel of a liquid crystal display device as a non-luminous device requires a back light unit because of a structure. A back light unit consists of various optical systems and the back light unit uses an optical film having regular arrangement to improve brightness.
FIGS. 1A and 1B are a diagram schematically illustrating a structure of a conventional liquid crystal display.
As shown in FIG. 1A, a back light unit 10 includes a light source 1, a reflector 2, a light guide plate 3, a diffusion sheet 4, a first optical sheet 5 and a second optical sheet 6.
The light source 1 is a device for generate a visible light and a light emitting diode (LED) and a cold cathode fluorescent lamp (CCFL) may be used as such light source 1 selectively.
Light emitted from the light source 1 is incident on the light guide plate 3 and the light travels in the light guide plate 3, while generating full reflection. The light incident on a surface of the light guide plate 3 at a predetermined incidence angle smaller than a critical angle is not full-reflected but transmitted to be emitted upward and downward.
At this time, the reflector 2 reflects the light emitted downward and makes the light re-incident on the light guide plate 3, only to improve light efficiency.
The diffusion sheet 4 diffuses the light emitted via a top side of the light guide plate 3 and makes brightness uniform. The vertical brightness of the light passing through the diffusion sheet 4 might be deteriorated.
The first optical sheet 5 consists of a disposing part 5a and a structural pattern 5b. The first optical sheet refracts and concentrates the light incident from the diffusion sheet 4 so that the incident light enters vertically into a surface of a second optical sheet 6.
The structural pattern 5b is integrally formed with a top side of the disposing part 5a and has a structure in order to refract the light incident via the disposing part 5a in a vertical direction to the second optical sheet 6.
The structural pattern typically has a triangle cross section and a vertex of the triangle shape is approximately 90°.
The shape of the second optical sheet 6 is the same as that of the first optical sheet 5. The second optical sheet 6 secondarily concentrates the light to enhance the brightness of the light primarily concentrated by the first optical sheet 5 and it emits the secondarily concentrated light.
Here, the first optical sheet 5 and the second optical sheet 6 are arranged to make crossed at right angles an extension direction of the structural pattern provided in the first optical sheet 5 and an extension direction of the structural pattern provided in the second optical sheet 6. The first optical sheet 5 is integrally bonded with the second optical sheet 6 via an adhesion layer 6a coated on a back side of the disposing part provided in the second optical sheet 6.
Meanwhile, as shown in FIG. 1B, once the first optical sheet 5 and the second optical sheet 6 are layered vertically to be bonded to each other via the adhesion layer 6a coated on the back side of the second optical sheet 6, an apex portion 5c is partially embedded in the adhesion layer 6a and the structural pattern of the first optical sheet 5 is integrally bonded with the second optical sheet 6.
However, a bonding rigidity is determined by a bonding area in which the apex portion 5c is embedded and bonded in the adhesion layer 6a and such a bonding area of the apex portion 5c is limited. Accordingly, there was a problem of deteriorating the bonding rigidity.
Also the bonding rigidity between the first optical sheet 5 and the second optical sheet 6 was deteriorated, resulting in the separation between the first optical sheet 5 and the second optical sheet 6 thereby. Accordingly, there was another problem of deteriorating a product yield.